Switching of spare repeater sections



Jan. 21, 1941. J p KENZER 2,229,090

SWITCHING OF SPARE REPEATER SECTIONS Filed Sept. 28, 1939 REGULAR FAG/LIT! FIG SPARE FACILITY SECTION SECTION P s74 r/o/v A .STA r/o/v B FazLom/vq s crasx 2, 5533 I Z fl AUX.

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L SPARE c l I 3 4 I AMP w D I F IG 3 STATION A REGULAR STATION 8 4MP INP GENE/M L- GENE/2A L- REGULAR IZED 1250 P TERfI/NAL SPA RE rEn i/A/AL L NETWORK F l NETWORK I c\ ZZZZT 0 LL REGULAR 4w AMP 2/ EV i i /6 G IAMPZ l2 SPARE C up 4502 F G 5 FIG. 6 A

L AUX. EMPE F C I STATION ,4 FIG 7 smr/o/v a 3 REGULAR 3 j@ o----' AMP w \B IN [/5 N 70/? A J P. K/NZER --------i v BY AMP MP D A TTOR/VE V Patented Jan. 21, 1941 PATENT OFFICE SWITCHING F SPARE REPEATER SECTIONS John P. Kinz'e'r, Ridgefield, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application September 28, 1939, Serial No. 296,891

'12 Claims.

This invention. relates to broad band transmission systems such as multichannel carrier current signaling systems.

Although the invention is applicable to open by, 'tvire circuits, wire cable and coaxial cable circuits, it relates to problems which become especially significant in circuits carrying a large number of signal channels, suchas coaxial cables. In such circuits it is customary to use a large 10 number of line repeaters in tandem spaced at intervals which may be as short as five miles or even less, with several unattended repeaters between attended repeater points, a section between such attended points being perhaps fifty or 15. one hundred miles long. If a failure or a degradation in the operation of any element or ele- 'ments in the circuit occurs, such as a tube failure, it q isually means that the whole facility fails or isiiegraded, and this may involve several hundred no signal channels in the circuit. Thus, incertain 'coaxial systems it is proposed to have as many as 400 or 500 channels on a single coaxial conductor. While with great precaution the likelihood of failures or degradations maybe verysmall, the number of channels involved renders it of the greater importance to make suitable provision in the event that they do occur.

In my invention I provide certain spare facilities and the purpose of 'the invention is to ar- 30 range for the substitution of such facilities in place of the regular facilities to such extent as is needed in case: of failure. Another purpose is to make this substitution in such manner as to reduce to a minimum any interruption or any ir- 3 regularity in the transmission of the various signals or types of signals which are being transmitted. This latter is a matter of importance where high speed telegraph is present, either alone or superposed on other signaling currents, the prac- 40 tical requirement being that the interruption shallbe something less than one millisecond.

The invention will be betterunderstood by ref eronce-to, the following specification and the accompanying drawing in which:

Fig. 1 represents in a schematic manner a signaling circuit adaptedfor broad band or multichannel signaling;

Fig.2 shows in some detail a circuit arrangement which may be used in one of the sections of 50 Fig. 1; and I Figs. 3 to 7 show various modifications of Fig. 2.

, Referring more particularly to Fig. 1, there is shown a view of thesections which may make up a broad band signaling circuit such as a coaxial 55 cable. Each section extends in general from one attended repeater point to the next attended re peater point and between these points there will be a plurality of repeaters which will normally be unattended but will be associated with the attended points. I

In accordance with my invention each section will comprise a regular circuit normally used for transmission over this distance. In addition, I provide in each section a. spare facility parallel to and substantially identical with the regular facil- 10 ity. In the event of failure or degradation beyond a certain amount of the regular facility, I replace it by the spare, thisreplacement being made by manual or electrical operation of suit- 3 able switches in a manner which introduces a '15 minimum amount of disturbance to any signals being transmitted at that moment. If the switching operation is performed electrically it may be from separate points or from a single point, such as an attended point. Furthermore, it may be initiated manually, on the appearance of some alarm signal, or automatically by relying on a change in a pilot signal present on the transmission circuit. The regular facility, having been removed from the transmission path, may be repaired or restored to normal action and then reintroduced, with removal of the spare facility.

In further detail, at the transmitting end of a section a hybrid coil H1 connects from the receiving end of the previous section to the transmitting end of the section in question. The output of the hybrid coil contains connections to both the regular and the spare facilities, the regular facility being connected at points I and 2 and the spare facility being connected at the points 3 and t. In. addition, in this terminal network there is included an impedance Z1. Switches A. and C are supplied across the inputs of the two facilities. The adjustment of impedances is such that if the switch C is closed placing a short across the input terminals of the spare, then signal voltage appears across the points I and 2. If, however, the switch C is opened, then signal voltage will, in general, appear across I and 2 and across 3 and 4.

At the receiving end of the section a second hybrid coil Hz is provided with one winding connected to the output of the regular facility. The output of the spare facility is one element of a network including the other windings of the hybrid coil and the impedance Z2. Switches B and D are connected acrossthe outputs of the two facilities and the adjustment of the impedanoes in the network is such that when the switch D is closed, thus shorting the output of the spare facility, signal voltage over the regular facility is impressed through the hybrid coil across the points 5-6, which are the input terminals of the transmitting end of the following section. If, on the other hand, the switch D is opened, then the signal arriving simultaneously over the regular and spare facility is transmitted to the next section.

Normally switches C and D are closed and A and B are open. Transmission takes place through the regular channel, but the spare facility takes no part in the signaling and may be removed for other purposes, if desired. To perform the switch the spare facility is patched in by the opening of switches C and D simultaneously, or as near simultaneously as possible, and the transmission then takes place over both regular and spare circuits. Switches A and B are now closed simultaneously and transmission is then through the spare facility only. The regular facility may now be disconnected for repairs or such other purposes as are desired.

Certain of the conditions which should preferably be met in any case are that the transmission shall be the same for the three possible paths of transmission, that is:

1. Through the regular facility only;

2. Through both regular and spare simultaneously;

3. Through the spare facility only.

The adjustment of impedances Z1 and Z2 may be made such that these conditions are met. In general there will be s0me loss incurred in the hybrids, in which event it may be desirable to incorporate an auxiliary amplifier shown at 8 in the output of the hybrid coil to compensate for the loss of level. Also in this circuit it may at times be advantageous to use open-circuiting switches to disconnect the facilities rather than the short-circuiting switches shown.

From a more general point of view it may be stated that what is desired are two six-terminal networks that will satisfy the conditions stated above. These generalizations are embodied in the schematic circuit of Fig. 3. Referring to that figure we may suppose that transmission is over the regular facility and that switches C and D are closed. If it is assumed that it is not feasible to operate switches C and D simultaneously for any reason, such as wide separation of the two switches, then for suitable operation it is necessary to fulfill the requirement; first, that the transmission from A to B shall be unchanged where either C or D only is opened. Second, the transmission must be unchanged when the other switch of this pair is opened, which will give transmission over the two parallel paths. Third, in order to remove the regular facility from service it should be possible to close either switch A or B without affecting transmission. Finally, it is necessary to close the other switch of the pair, also without affecting transmission. Analysis of the circuit leads to the conclusion that the first and thi d of the conditions will be met if the points A and C are conjugate to each other, or if points B and D are conjugate. One method of fulfilling the second requirement is to make point A conjugate to point F when switch C is opened and not conjugate to F when switch C is closed. The fourth requirement can be met if point A is conjugate to point F when switch C is opened.

These considerations lead to a specific modification of Fig. 2 which I find particularly useful for carrying out my invention. This is shown in Fig. 4 in which the impedance Z1 is so chosen that the points F and A are conjugate when switch C is opened. For the usual hybrid coil with same number of turns or the same inductance in windings II and I2 this means that Z1 equals the impedance looking to the right from point C.

The impedance Z2 is so chosen that the points B and D are conjugate. For the usual hybrid where winding It has n times as many turns or n times the inductance of windings l4 and I5 together, this means that times the impedance looking to the right of point G. With these conditions fulfilled the operation of the circuit is as follows:

1. Switches A and B are opened, C and D are closed. The energy coming from the amplifier at point F divides between the impedance Z1 and the regular circuit at point A. The energy going into Z1 is dissipated and the remainder goes over the regular facility. The energy coming from the output of the amplifier at B divides between impedance Z2 and the circuit at point G.

2. Switch D is now opened. Since points B and D are conjugate, the transmission from B to G is unchanged and the over-all transmission is also unchanged.

3. Switch C is now opened. The energy from the output of amplifier F now divides equally between Z1 and the circuit at C. There is no input to the circuit at A and consequently no transmission over the regular facility. However, transmission now takes place over the spare facility. As the spare facility is similar to the regular facility in its transmission properties, the output of the amplifier at D is the same as the former output of the amplifier at B. The energy coming from the output of the amplifier at D divides between impedance Z2 and the circuit at point G in the same ratio as formerly. Thus, the over-all transmission remains the same as previously.

4. Switch B is now closed. Since B is conjuate to D, this has no effect on the transmission from D to G.

5. Switch A is closed. Since F and A are conjugate, this does not affect the transmission from F to C.

6. With switches A and B closed the regular facility may now be patched off.

7. In transferring from spare to regular, the procedure would be in the reverse order as follows: (1) open A, (2) open B, (3) close C, close D.

If the direction of transmission is reversed, so

as to be from right to left by reversing the amplifiers, the same sequence of operations will successfully perform the switching operation.

One of the marked advantages of this circuit arrangement of Fig. 4 is that no switches need to be made simultaneously. That is, only one switch need be operated at the time. At any instant signal is carried by one circuit only and transfer to the other circuit takes place, with no appreciable delay, on the operation of one parhybrid coils are shown but they are replaced by bridges in which the arms may be purely resistive or may be reactive elements. The bridge at the receiving end is balanced so that B and D are conjugate. The bridge at the transmitting end is balanced if C is open, and then F and A are conjugate. The sequence of operation of the switches is the same as that described in connection with Fig. 4.

A further modification for the circuit at the receiving end of the section is shown in Fig. 6. The impedance Z2 is made equal to the impedance ZA looking into the auxiliary amplifier and the transformer is made of unity turns ratio. Under these conditions the points B and D are conjugate and the transmission from B to G and from D to G are equal. This is because the voltage drop across Z2 is equal to the voltage drop across ZA (assuming transmission from B to G). The transformer is so poled that the voltage across the winding 3-4 opposes the voltage across ZA. This results in zero voltage across the output of the amplifier at D during transmission from B to G.

Still a further modification of my invention is shown in Fig. 7. This circuit is characterized by the fact that the hybrid coil at the transmitting end of the section is avoided, the spare facility being bridged across the line through a high loss pad Ill with an amplifier A7. The bridging pad causes a negligible loss in the transmission through the regular facility when bridged across the regular transmission line. Such a bridging path may be left permanently connected or may be bridged without interruption of the transmission because of the negligible loss which it introduces. The bridging amplifier A7 compensates for the loss in the bridging pad, the combination of the pad and the amplifier having essentially zero equivalent.

At station B the switch D is normally closed and switch B open so that the power from the amplifier at B divides between Z2 and G. When switch D is opened point B becomes conjugate with point G so that transmission now takes place from D to G and none from B to G. Switch B can now be closed and the regular facility disconnected at station B. Points B and G may be made conjugate by making Z2 equal to the impedance looking to the left from switch D. Suitable adjustment of the transmission through the two facilities should be made so that power transmission from B to G with switch D closed equals that from D to G with switch D opened.

It is apparent that if the regular facility at station A is to be disconnected after switching, it is necessary to provide apparatus to substitute a termination across the bridging pad equal to the impedance of the facility. Such a termination is shown schematically at Z4.

While I have illustrated my invention with a number of alternative forms of circuits, it will be observed that they all meet certain broad requirements and it is apparent that within these requirements various other circuit modifications can be made without departing from the spirit of this invention. It will be observed also that while the invention has been described primarily in terms of two stations, A and B, which may be widely separated and linked with a transmission circuit including a plurality of repeaters and other equipment, that it could be equally well applied to the substitution of any single piece of equipment for another piece, such, for example, as the replacement of one repeater by another repeater, the switches being all physically close together.

What is claimed is:

1. In a transmission line, a regular facility and a spare facility in said line, means for so associating these to the line at the transmit end and at the receive end of the facilities that the transmission shall be the same whether over the regular facility alone, over both regular and spare simultaneously, or over the spare alone, and that the transition from the one condition to the other shall be smooth.

2. In a transmission line, a regular facility and a spare facility which may be substituted for the regular facility, a six-terminal network at the transmit end of'the facility with one pair of terminals F connected to the line going to the facility, one pair A to the input of the regular, and one pair C to the input of the spare facility, the network being such that with the pair C inoperative for transmission, transmission takes place to A and with C operative for transmission, no transmission takes place to A.

3. The combination of claim 2 characterized by the fact that the pair C is rendered. inoperative by being shorted and that when the pair C is unshorted, the pair A is conjugate with respect to the pair F.

4. In a transmission line, a regular facility and a spare facility both normally connected in the transmission line, means for so associating these to the line that the one may be substituted for the other, said means comprising a six-terminal network at the receive end of the facility with one pair of terminals G connected to the line going out from the facility, one pair B to the output of the regular facility, and one pair D to the output of the spare facility, the network being such that with the pair D shorted transmission takes place from B, and with D opened transmission takes place therefrom but no transmission takes place from B.

5. In a transmission line, a regular facility connected between two points and a spare facility adapted to be substituted therefor, means for associating the facilities to the line comprising a six-terminal network at the transmit end of the facilities with one pair of terminals F connected to the line coming to the facility, one pair A to the input of the regular, and one pair C to the input of the spare facility, the network being such that with the pair C inoperative for transmission, transmission takes place to A and with C operative for transmission, no transmission takes place to .A, a second six-terminal network at the receive end of the facilities with one pair of terminals G connected to the line going out from the facility, one pair B to the output of the regular, and one pair D to the output of the spare facility, the network being such that with the pair D inoperative for transmission, transmission takes place from B to and with D o erative fo transmission, no transmission takes place from B to G.

6. The combination. of claim 5 characterized by he fact that the six-terminal networks are so adjusted that the terminals A are conjugate to the terminals F when terminals C are prepared for transmission and the terminals B are conjugate o the terminals D.

'7. In a communication system comprising a section of broad band signaling line subject to impairment of service, an identical section serving as a spare, means for substituting the spare section for the regular section, said means comprising at the transmitting end of the section a hybrid coil and network connection from the previous section to the regular section and its spare whereby when the spare is connected the regular section is conjugate to the previous section and a hybrid coil and network connection from the output of the regular and of the spare section to the next line section such that the output circuits of the regular and the spare are conjugate to each other.

8. In a communication system comprising a section of broad band signal lines subject to impairment of service, an identical section serving as a spare, and means whereby the spare may be substituted for the regular section, said means comprising a network at one end of said section and respective signal transferring connections therefrom extending between each of said sections and a preceding line section, a network at the other end of said regular and spare sections and respective signal transferring connections therefrom extending between each of said regular and spare sections and a succeeding line section, respective shunting contactors across said several connections, and means for operating said contactors to shunt alternatively said regular and spare sections, whereby said regular section can be replaced by said spare section while maintaining series continuity of signaling circuits.

9. lhe combination of claim 4 characterized by the fact that the transmit end of the regular facility is connected for normal transmission and the spare facility is bridged across the transmission line through a bridging pad, introducing negligible loss in transmission through the regular facility, the bridging pad in the spare facility being supplemented by an amplifier to make up its loss.

10. In a transmission line, a regular circuit connected between two points and a spare circuit adapted to be substituted therefor, means for associating the circuits to the line comprising a six-terminal network at the transmit end of the circuits with one pair of terminals F connected to the line incoming to the circuit, one pair E to the input of the regular circuit and one pair C to the input of the spare circuit, a second six-terminal network at the receive end of the circuits with one pair of terminals G connected ot the line going out from the circuits, one pair E to the output of the regular and one pair D to the output of the spare circuit, the networks being such that transmission over both regular and spare circuits simultaneously is identical to that over either line.

11. A communication system comprising a oneway repeatered section of broad band signaling line subject to impairment of service, an identical like-directed one-way repeatered section of line serving as a spare, a six-terminal network at the transmit end of said sections of line connecting said sections in signal transfer relation with the preceding portion of said system and in conjugate relation with each other, and means at the receive end of said sections of line for connecting them alternatively in signal transfer relation with the succeeding portion of said system.

12. A combination in accordance with claim 11 in which said means at the receive end comprises a six-terminal network, a connection from two pairs of the network terminals to the receive ends of the respective sections of signaling line, a connection from the third pair of terminals to the said succeeding portion of the system, circuit interrupting contactors in said first-mentioned connection normally disabling the said connection to said spare section of line and enabling the said connection to the other of said sections, and means for substantially simultaneously interchanging the condition of said contactors whereby said spare section is substituted in circuit, said network being such that transmission over both of said sections simultaneously is substantially the same as that over either alone.

JOHN P. KINZER. 

